Tracheal Rapid Sequence Intubation

Anatomy and Physiology

Assessing Airway Risk

Several parameters need to be evaluated before the start of the procedure. Multiple mnemonics, including L.E.M.O.N., exist to help a clinician determine if an airway will be difficult.[2]

• L: Look externally (facial trauma, beard, loose teeth, dentures, large incisors); these factors can indicate a difficult airway.

• E: Evaluate the 3-3-2 rule
  • Can 3 fingers fit between the incisors?
  • Can 3 fingers fit between the tip of the chin and the hyoid bone?
  • Can 2 fingers fit from the top of the thyroid notch to the hyoid bone?
  • A decrease in these distances can be an indication of a difficult airway.

• M: Mallampati score; assess how much of the posterior pharynx and uvula can be seen (a higher Mallampati score indicates a more difficult airway).
  • Mallampati 1 score: Indicates that the entirety of the uvula can be visualized
  • Mallampati 2 score: Indicates that half of the uvula can be visualized
  • Mallampati 3 score: Indicates that only the base of the uvula can be visualized
  • Mallampati 4 score: Indicates that the uvula cannot be visualized

• O: Obstruction or obesity
  • Obesity (body mass index >30) can predict a difficult airway.
  • Obstruction of the airway, including head and neck cancer and epiglottitis, can indicate a difficult airway.

• N: Neck mobility
  • Assess the neck's mobility; a neck that cannot be maneuvered into an ideal position due to trauma, a C-collar, or rigidity can lead to a more difficult airway.

Positioning and Anatomy

Proper patient positioning is vital to the success of the procedure. Ideally, the neck should be flexed at the lower cervical spine (C6-C7) and extended at the upper cervical spine (C1-C2). This position is called the "sniffing position." It allows for the best visualization of the anatomy, including the epiglottis and vocal cords (see Image. Sniffing Position).

The epiglottis serves as the primary landmark that will direct successful endotracheal intubation. The origin of the epiglottis can be found at the base of the tongue. The valley between the tongue and the epiglottis is called the vallecula. When intubating with a Macintosh blade (discussed later), the tip of the blade should ideally be placed at the base of the tongue in the vallecula, and a ventral and inferior movement of the blade reveals the vocal cords. 

The Cormack and Lehane Grading system allows the provider to evaluate their view of the vocal cord and estimate the chance of successful intubation. A Grade 1 view of the cords using this system indicates a high likelihood of successful intubation. In this grade, the provider can see nearly the entirety of the vocal cord anatomy. Successive grades reveal fewer cords and a decreased rate of successful intubation (see Image. Cormack-Lehane Grading System).

Indications

RSI is indicated for a patient in acute respiratory failure due to poor oxygenation or ventilation and for a patient who cannot protect their airway due to altered mental status. RSI may also be used in a patient with an acute upper gastrointestinal bleed with a high risk of aspiration.[3]

Contraindications

There are few absolute contraindications for rapid sequence intubation. These contraindications include complete upper airway obstruction and the loss of facial or oropharyngeal landmarks, which will require a surgical airway to be placed.

Relative contraindications are related to issues that may lead to procedural failure, which can be due to injuries to the airway, anatomic abnormalities, and the proficiency of the clinician.[4] These relative contraindications can be evaluated using the L.E.M.O.N. mnemonic and Cormack and Lehane Grading system discussed above.[5]

Equipment

There are many supplies necessary in preparation for rapid sequence intubation:

•  Endotracheal tube with an inflatable cuff with sterile lubricant
•  Laryngoscope handle and blades
•  Suction (x2)
•  Bag valve mask
•  End-tidal carbon dioxide monitor
•  Induction agents
•  Tracheal tube inducer (bougie)
•  Supraglottic airway, such as laryngeal mask airway
•  Video-assisted laryngoscopy
•  Pulse oximetry
•  IV access
•  Push dose pressors (see Image. Equipment for Endotracheal Intubation).[6][7]

Before initiating the procedure, the clinician should ensure adequate lighting for the room. The clinician should test the lighting source on the laryngoscope and the inflation of the endotracheal tube. An easily viewed pulse oximeter should also be available.

Endotracheal Tube Size

Generally, a 7.0- to 7.5-mm internal diameter tube should be placed in a female patient, and a 7.5- to 8.0-mm tube should be placed in a male. Smaller tube sizes are not adequate for performing a bronchoscopy if necessary.

Blade Selection

The most commonly used laryngoscope blades are the Macintosh and Miller blades. The Macintosh blade has a curved spatula used to approximate the curvature of the tongue and move the epiglottis, mandible, hyoid bone, and other soft tissues out of the view of the glottis (see Image. Superior View of the Glottis). A Macintosh 3 has a 13-cm blade and fits most average-sized adults. A Macintosh 4 blade is 15.5 cm, allowing the practitioner to utilize a longer blade if necessary. The Macintosh blade should be placed inside the vallecula at the base of the tongue. A flat Miller blade is designed to go over the epiglottis to reveal the vocal cords. 

Induction Agents

An in-depth discussion of the agents used to induce and paralyze patients undergoing RSI is outside the scope of this article.  However, below are two charts of the frequently used induction and paralytic agents and their differing characteristics (see Image. Induction and Paralytic Medications).

Technique or Treatment

Once the patient, supplies, and team have been properly prepared, induction agents can be administered to the patient first, followed by paralytic agents (see Image. Induction and Paralytic Medications). The bag valve mask should be utilized to pre-oxygenate the patient as much as possible. The clinician performing the rapid sequence intubation should ensure a tight seal of the bag valve mask to the patient's face.[8]

After allowing the paralytic agents to take effect after 60 seconds, the patient's mouth should be opened with the scissoring technique. The scissoring technique involves placing the right thumb on the right middle finger and inserting the right hand into the patient's mouth. The clinician then "scissors" the patient's mouth open, crossing the thumb and middle finger. The laryngoscope should then be inserted into the patient's mouth with a sweeping motion from right to left, moving the tongue out of view.

The clinician should locate the epiglottis and place the laryngoscope in the vallecula. A ventral and inferior motion should be performed with a rigid wrist without abduction or "rocking" of the wrist. Suctioning can be performed to obtain a better view and clear debris, and pressure can be applied to the thyroid cartilage to manipulate the glottis into view. Once the clinician has located the glottis, the endotracheal tube can be passed through the vocal cords. Once passed, the stilette can be removed from the endotracheal tube. The tube should be advanced based on the Chula formula: endotracheal tube depth=0.1 (height in cm) + 4. This equation will give the depth at which the endotracheal tube should be advanced when measured at the patient's teeth.

The cuff should be inflated after the tube is advanced to the proper distance. End-tidal capnography, condensation on the endotracheal tube, and bilateral lung sounds should all be used to verify placement initially. A chest X-ray should be performed to assure adequate placement.[9]

Complications

Multiple tools can be used when the clinician cannot place the endotracheal tube with direct laryngoscopy using the standard technique.

• A video-assisted laryngoscope can be used to view the glottis better. 
• A grade 4 Cormack and Lehane view of the anatomy may prompt the clinician to utilize the tracheal tube inducer or bougie. A bougie is a long rod-shaped medical device with a curve at the tip. This item is introduced into the patient’s airway, and an attempt is made to place the tube inside the trachea. If the bougie is swept along the trachea's wall, the tracheal rings' signature ridges can be felt. The endotracheal tube can then be introduced over the bougie, and the bougie will guide the endotracheal tube into the trachea.
• A supraglottic airway, such as a laryngeal mask airway, can be placed if endotracheal intubation is not possible.[10][11]

Enhancing Healthcare Team Outcomes

At least 2 to 3 medical professionals must manage the airway for rapid sequence intubation. A clear delineation of roles is necessary for successful endotracheal intubation. The lead clinician is responsible for directing the team, managing the patient's airway, and intubating the patient.

A nursing staff member is responsible for providing induction and paralytic medications at the onset of the procedure. The nurse should wait for the clinician performing the intubation to give their approval before administering medications. An independently trained clinician who can procure equipment, operate the bag valve mask, apply cricoid pressure, and confirm tube placement after the intubation is completed should also be at the bedside. Discussion and preparation for a backup plan in case of procedure failure should be addressed before the start of the procedure.